In recent years the rapid adoption of wireless communication technology has triggered a rapid increase in the ability of people to conduct their lives whilst on the move. Technological advances resulting in a combination of compact, low power, efficient, high speed, and ergonomically designed microprocessor based portable devices with advanced communications have spearheaded this adoption. With each generation, better, more user friendly or more advantageous features are added. Present wireless communication devices support a wide variety of applications including: World Wide Web access, text messaging, voice communications, address book management, scheduling, alarm clock, electronic mail, camera, video camera, video conferencing, and so forth. Only a few years ago, many of these features were only available on a desktop computer system.
New features and applications are released, typically every year. For example, present systems now support the procurement and presentation of multiple media formats, including MPEG music, streamed video, news stories, and even books, through to the online purchase of items directly from company websites or other locations. This is now coupled with other facilities designed to make life easier for people on the move, and coincidentally acts to lower individual and corporate installation requirements for each office. This often results in lower office space requirements and in lower staffing requirements.
In most of these applications and others, there exists the requirement to transfer information in a secure manner. This need is driven from both ends of the communication path, for example, either from the users' viewpoint of providing bank account details, credit card numbers etc through to the service provider who seeks to similarly protect confidential information but also limit the dissemination of procured media content thereby reducing theft.
Common to many security techniques are encryption mechanisms wherein data to be transmitted is obfuscated—transformed to seemingly meaningless information—through an encryption process utilising encryption keys which are either separately communicated or synchronized to allow the information to be reverse-transformed—recovered—after transmission via an insecure medium, such as the Internet. Different approaches are known using public and private key forms, multiple keys, and even multiple keys to encode different sections of the same information.
Some encryption processes require that the encryption key is expanded prior to use. When key expansion is necessary, these keys are stored in their expanded form during use so that the expanded keys are readily available and processing time for key expansion is not necessary during the ciphering process. For a system managing for example multiple network data traffic flows simultaneously, such a pre-expansion is beneficial to ensure that system performance is not affected when context switching occurs. As such, when in common use, each key is stored both in its initial form and in its expanded form. Such approaches therefore require additional memory resources for the storage of the extracted keys but save processing time for extracting those keys repeatedly during use. Such approaches also have inherently lower security as an unauthorized access to the device or memory may extract all or some of the expanded encryption keys.
For the manufacturers of many portable devices there is benefit in being able to lower the memory requirements of these devices, both to reduce cost of the memory itself but to also reduce the power consumption of the memory and increase the stand-by or active life of the device before requiring recharging. Such benefits are advantageous where they do not come at the expense of overall performance of the portable device.
It would therefore be advantageous to use a ciphering process that reduces memory storage resource requirements but provides approximately equivalent performance.